One of the existing methods of producing medium to large quantities of metal tubing is through the use of pilger mills, also known as tube reducers. Another method to produce metal tubing is cold drawing but it is typically only used for small quantities of tubing. Pilger mill machines have been producing metal tubing since 1880 and are considered to be an efficient manufacturing process for significant quantities. The fundamental methods to form tubing from the pilger mill is with the use of an upper and lower die, rolling back and forth over a mandrel. This method was established in 1880 by the Mannesmann brothers of Germany when they patented a hot working of tubes.
In 1896, an American engineer patented the first cold pilger mill. The process principle has not changed since then but the supporting mechanisms have changed over the years many times. Many patents have been issued using new technology to support the same pilger principle. As the pilger principles utilize tooling to reduce the tube products, supporting mechanisms within the current day process are vital and crucial to the updated functions.
In general, each pilger machine has a major drive mechanism that provides a linear motion to the tooling, known as a stroke. Many of the machines in use today use a crankshaft for the linear movement. As the tooling consists of an upper & lower die that rolls back and forth over the tube product. A stationary rotating mandrel is located within the tube inside diameter.
Both top & bottom dies have a pre-shaped groove which forms or re-shapes the tube product smaller on each stroke. As the top & bottom dies form the outside diameter of the tube to a smaller size, the mandrel and the dies together also work the tube wall into a smaller size. As the dies roll back & forth, the tube product is fed into the dies and over the stationary rotating mandrel. While the tube is reduced in size of outside diameter and inside diameter, the tube also becomes elongated.
The supporting mechanisms that provide the vital functions on today's pilger mills are done thru the use of various gearboxes. All of these current gearboxes provide 3 basic functions directly to the incoming tube for the typical pilger process. They provide tube turning (or indexing), incremental feeding, and bumping of the incoming tube over the rotating mandrel. The stationary mandrel rotation is also provided by two of the gearboxes and is mechanically driven from within the gearboxes.
Current pilger mill machines perform these three functions, along with pilgering (forming) the tube, for a continuous operation. A continuous operation means that the pilger machine operates without stopping the machine to load new incoming tubes. Older generations of pilger mills have to stop and load one tube and then operate for that one tube, then stop to load the next incoming tube.
As a continuous pilger mill operation, many of these machines have 4 gearboxes that service the previously mentioned functions, turning, feeding and bumping. One gearbox, referred to as an upper gear train gearbox, transfers the rotary motion from a crankshaft, or other rotary drive, to three other gearboxes via a line shaft mechanism. A second gearbox, as driven by the line shaft, transfers the rotary motion into turning of the incoming tube and mandrel lock. The third gearbox, as driven by the line shaft, transfers the rotary motion into turning of the incoming tube. Also, this third gearbox provides feeding and bumping of the incoming tube as well as operating a mandrel lock. The forth gearbox, as driven by the line shaft, transfers the rotary motion into turning of the incoming tube. Also, this forth gearbox provides feeding of the incoming tube.
As described in U.S. Pat. No. 5,035,132 by Josef Gerretz, multiple gearboxes were used in order to achieve a continuous operation of the pilger mill. These multiple gearboxes provided the necessary feeding and turning of the incoming tubes. Other related patents enhance this continuous mill operation. The disadvantage to this patent is that it does not perform any of the necessary bumping of the tube products which is very important to many of the pilger processes. Also, this patent fails to describe how the device grips the tube product.
As described in U.S. Pat. No. 6,257,040, by Michael Beansch, Wolfgang Ernhardt, Bernhard Gromada, Ernst Holler, Horst Mattes, the inventors replaced the older mechanical drives of the 1960s with updated technology. The improved controls of the hydraulic drives, are an improvement to the pilger process. These drives still provide the same necessary feeding and turning of the incoming tubes in all of the gearboxes. The disadvantage of this patent effort is it still requires multiple gearboxes.
Other related patents continue to promote or enhance the continuous pilger mill operation using two or more gearboxes to support the necessary feeding & turning of the tube into the pilger tooling. The disadvantage of the use of multiple gearboxes is the large cost of operation and maintenance that is required to maintain the necessary supporting functions of feeding & turning. A large percentage of the initial cost of investment into a pilger mill is in the complex gearboxes. Also, the maintenance cost of two or four gearboxes is staggering over time as the machine experiences normal wear.
Accordingly, there is a need for a pilger mill device that performs the necessary functions of indexing, feeding, bumping and mandrel rotation with fewer gearboxes. The present invention satisfies this need and provides other related advantages.